BEIJING—China's economic growth slowed again in the second quarter, a deceleration that will test Beijing's resolve to avoid fresh stimulus measures, even as evidence of a stalled rebalancing toward consumer-driven growth underlines a need for deeper reforms.

Gross domestic product grew 7.5% in the second quarter compared with a year earlier, down from 7.7% in the first three months of the year and in line with expectations, the Chinese government's statistics bureau said Monday. On a quarter-on-quarter annualized...